My Anon M2's with an extra lens in my coat or backpack (I have the standard lenses - Red Solex for bright conditions and Blue Lagoon for dim/flat). Someone above mentioned easy lens changes on the Smith I/OX, but that's got nothing on the Anon. I change mine in a few seconds without taking my goggles off.
I second the Anon M2. I carry the same to lenses and the ease to swap lenses is outstanding. It takes longer to take the spare lens from your pocket than to swap them. Once you have the lens out, it literally takes about 3 seconds (not an exaggeration) to take off the current lens and put the new one on (without taking your goggles off). They also fit very comfortably. Also, next year, Anon M2 will get MFI (face mask that attaches to the goggles with magnets), so I'll likely upgrade to those next year; super pumped!